Transistors are pervasive in today's society. Transistors form the building blocks for almost all commercial semiconductor products. Through use, the operation of a transistor may degrade over time. There are currently several known modes of transistor degradation. One type of degradation mechanism involves channel hot carriers. In general a high electric field within a transistor causes degradation in the gate oxide. Another degradation mechanism is referred to as negative biased temperature instability degradation.
Current methods for measuring transistor degradation involves CMOS ring oscillators. In general, a ring oscillator formed from an odd plurality of CMOS inverters is operated at excess voltage levels and the frequency resulting from the oscillator is measured over time. As transistors within the CMOS inverters degrade, the frequency generated by the oscillator slows down. Thus the measured frequency of the oscillator provides a measure of the overall degradation of the transistors in the CMOS inverters.
A problem with this approach is that, although it provides an overall measure of the degradation within transistors, it does not allow an identification of the magnitude of contribution of the various constituent degradation mechanisms. Knowing the magnitude of each constituent degradation mechanism allows better modeling of transistor degradation.